MyBatis 实现一对一，一对多关联查询，java 程序设计教程课后题
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
[](
)在 application.yml 文件中进行数据库和 mybatis 配置
spring 配置
spring:
数据库配置
datasource:
type: com.zaxxer.hikari.HikariDataSource
url: jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&autoReconnect=true&allowMultiQueries=true&useSSL=false&tinyInt1isBit=false&serverTimezone=GMT%2B8
driverClassName: com.mysql.cj.jdbc.Driver
username: root
password: root
mybatis 配置
mybatis:
给实体类配置别名
type-aliases-package: com.jourwon.*.pojo
加载 mybatis 的 mapper 配置文件
mapper-locations: classpath:mybatis/mapper/**/*Mapper.xml
configuration:
开发环境控制台打印 sql 语句
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
开启驼峰规则自动映射字段属性值；如字段为 user_name 的可以映射到 userName 属性中
map-underscore-to-camel-case: true
设置 sql 执行超时时间,以秒为单位的全局 sql 超时时间设置,当超出了设置的超时时间时,会抛出 SQLTimeoutException
default-statement-timeout: 30
解决查询返回结果含 null 没有对应字段值问题
call-setters-on-nulls: true
[](
)新建老师类 Teacher
@Data
public class Teacher {
private int id;
private String name;
}
[](
)新建班级类 Classes
@Data
public class Classes {
private int id;
private String name;
private Teacher teacher;
private List<Student> studentList;
}
[](
)新建学生类 Student
@Data
public class Student {
private int id;
private String name;
}
[](
)新建 ClassesMapper.xml 映射文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.jourwon.mybatis.mapper.ClassesMapper">
<select id="listClasses" parameterType="int" resultMap="ClassesResultMap">
select * from classes c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>
<resultMap type="com.jourwon.mybatis.pojo.Classes" id="ClassesResultMap">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.jourwon.mybatis.pojo.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
</resultMap>
<select id="listClasses2" parameterType="int" resultMap="ClassesResultMap2">
select * from classes c,teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}
</select>
<resultMap type="com.jourwon.mybatis.pojo.Classes" id="ClassesResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.jourwon.mybatis.pojo.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="studentList" ofType="com.jourwon.mybatis.pojo.Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>
</mapper>
[](
)Application 类
@MapperScan(basePackages = {"com.jourwon.mybatis.**.mapper"})
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
[](
)测试类
@RunWith(SpringRunner.class)
@SpringBootTest
public class ApplicationTests {
@Autowired
private ClassesMapper classesMapper;
/**
Description: 测试班级与老师一对一关联关系
@author JourWon
@date 2019/9/24 23:18
@param
@return void
*/
@Test
public void test01() {
List<Classes> classes = classesMapper.listClasses(1);
for (Classes aClass : classes) {
System.out.println(classes);
}
}
/**
Description: 测试班级与学生一对多关联关系
@author JourWon
@date 2019/9/24 23:19
@param
@return void
*/
@Test
public void test02() {
List<Classes> classes = classesMapper.listClasses2(1);
for (Classes aClass : classes) {
System.out.println(classes);
}
}
}
[](
)测试结果
test01()测试结果输出
==> Preparing: select * from classes c,teacher t where c.teacher_id=t.t_id and c.c_id=?
==> Parameters: 1(Integer)
<== Columns: c_id, c_name, teacher_id, t_id, t_name
<== Row: 1, 高三 2 班, 1, 1, 老师张三
<== Total: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@140d1230]
还未添加个人签名 2021.03.18 加入
还未添加个人简介
评论